A self-expanding stent is typically introduced into the body using a delivery device that includes an outer sheath coaxially disposed and slidable over an inner catheter. The stent is disposed at the distal end of the device between the inner catheter and the outer sheath and held in a compressed position by the outer sheath. The inner catheter and the outer sheath move coaxially with respect to each other. The stent may be deployed by proximally pulling back the outer sheath relative to the inner catheter until the stent is exposed. The self-expanding stent expands from the stent distal end to the stent proximal end as the sheath is proximally withdrawn.
Several problems may occur with the sheathed delivery device described above. The sheath release delivery devices are difficult to reposition or remove and slow to operate. The stent may only be partially deployed prior to reconstrainment of the stent by the sheath in order to still reposition or remove the stent. Once the stent is fully deployed, i.e. radially expanded, the sheath cannot reconstrain the stent. For example, utilizing a conventional outer sheath/inner catheter delivery device may cause the physician to inadvertently use excessive force and pull back the outer sheath too far, thereby prematurely deploying the stent in an incorrect position within a body lumen. At this step in the procedure, repositioning of the stent becomes difficult, if not impossible, because the stent has already radially self-expanded into the body lumen. Additionally, retraction of the outer sheath may not be achieved with controlled movement because the physician is manually retracting the outer sheath which may lead to uneven or inadvertent jerking back of the outer sheath that can lead to improper positioning of the stent.
Additionally, in a typical sheath release device where the outer sheath is proximally withdrawn, the first portion of the self-expanding stent to make contact with the body vessel is the most distal portion of the stent. This type of release may cause difficulty in accurately placing the proximal portion of the stent because the distal end of the stent is positioned first while the proximal portion of the stent is still covered by the outer sheath. Accurate placement of the proximal portion of the stent and/or the stent body may be important in certain applications, for example to prevent stent migration or to properly open a stricture along the entire length of the stricture. An additional drawback occurs with the sheathed stent delivery system where direct visualization of the stent is required. For example, in endoscopically placed stents, the sheath tends to prevent or obscure the location of the stent, making accurate placement of the stent more difficult.
Further potential drawbacks for the conventional sheathed stent delivery system involve the stent placement within the system prior to use within a patient. Loading and anchoring of a conventional sheathed stent delivery device is an involved process that may require preloading the stent into the device so that the stent remains compressed within the sheath during shipment and storage prior to use in the patient. Extended compression of the stent may lead to an alteration in the stent mechanical properties.
Conventional sheathed stent delivery devices also require a high force to overcome the friction between the stent and the sheath that may also be a problem for proper stent placement within the patient. The introducer must be mechanically stronger to overcome the frictional forces to avoid undesirable frictional consequences such as stretching of the introducer catchers and hysterics in the movement of the stent. The sheathed stent delivery device also requires more space within an endoscope compared to a sheathless device and also adds additional expense to the delivery system.
Accordingly, in view of the drawbacks of current technology, there is a desire for a mechanically expandable delivery system and dilation system that can increase the control, accuracy and ease of placement of a stent during deployment of the stent within a patient or dilation of a lumen within a patient. The delivery system would ideally reduce the risk of malfunction while providing for a smoother, more accurate and quicker deployment of the entire stent. The delivery system also would provide the ability to reconstrain, recapture, reposition and/or remove the stent after expansion of the stent.